Numerical study of Bragg resonance reflection for wave energy converter arrays in a two-dimensional viscous wave tank

Abstract

Bragg resonance occurs when the spacing between periodic coastal structures is approximately half the incident wavelength, which significantly reduces the energy extraction efficiency of wave energy converter (WEC) arrays. This effect was studied by establishing a quasi-two-dimensional viscous numerical wave tank (NWT) using a computational fluid dynamics (CFD) approach to simulate nonlinear wave interactions with a linear array of three floating WECs. Following convergence analysis and model validation, the wave propagation, dynamic responses and energy capture characteristics of the array were evaluated under three conditions: fixed, freely heaving, and energy-extracting. Bragg resonance occurred at 2S/L = 1.2 in the fixed case and at 2S/L = 0.9 in the moving case, corresponding to phase-up and phase-down shifts, respectively. Under energy-extracting conditions, a substantial power reduction of up to 53.1 % was observed during resonance, with the first and third WECs oscillating in phase and the middle WEC in counter-phase. The adverse effect of Bragg resonance on power output became more pronounced with increasing power take-off (PTO) levels. These findings offer practical insights for the design of floating breakwaters and the optimization of WEC array configurations to improve energy performance.